A screw is a fastener is a type of fastener characterized by a helical ridge, known as an external thread or thread, wrapped around a cylinder designed to cut a helical groove in a softer material as the screw is inserted. Commonly screws are used to hold objects together and to position objects. A screw has a head by which it is turned and thereby driven into the objects.
By contrast, a nail is a type of fastener which is driven into the objects by an axial blow or series of axial blows.
Concrete is a common construction material which is widely used for a variety of purposes including structural members, walls, floors, beams and the like. Concrete is a hard composite material including coarse granular components embedded in a hard matrix being the cement that fills the space among the aggregate particles and glues them together. Concrete is not malleable, ductile or resilient and is not known to permit plastic deformation of any kind once hardened. Similar to masonry and brick, concrete is considerably harder than most materials used for typical fasteners and is cut, drilled or threaded by vary hard abrasives or destructive impact tools. As such, concrete has a degree of non-uniformity which makes it difficult to precisely re-form, as by cutting and drilling, particularly on modern construction sites. This is particularly so when other building materials are to be attached or secured to a concrete member on site. Most often a pilot hole is required which would necessarily be irregular by reason of manual high-speed drilling tools such as a hammer drill or masonry bit. Such a pilot hole would have a nominal diameter and internal irregularities, which would include loose, partially detached and fully detached elements which could reduce or increase the nominal diameter.
The very hardness of concrete members and a high resistance to compressive forces makes on site attachment of other objects a common task which remains a time consuming, expensive and risk prone construction activity. This requires skilled labor and care in relation to supply of parts and their installation, both in relation to the object attached to the concrete, and the concrete itself.